As in most young animals (Scriber and Slansky, 1981; White, 1985) the dietary requirements of young cockroach nymphs differ from those of older nymphs and adults. Cochran elegantly demonstrated this in his studies of Parcoblatta spp., cockroaches that void urates to the exterior in discrete pellets if dietary nitrogen levels exceed a certain "break even" point with respect to nitrogen demands. In nymphs less than 1 mon old, a diet of 4% nitrogen results in only minimal urate excretion. On the same diet, nymphs 1 -2 mon old void urates at a rate of 8-13% of excreta by weight and large nymphs reach an equilibrium at less than 1.5% nitrogen in the diet (Cochran, 1979a; Cochran and Mullins, 1982). In nu merous species, this high requirement for nitrogen is reflected in the behavior of neonates, whose first meals are largely derived from animal or microbial sources. In many species the first meal consists of the embryonic membranes and the oothecal case. The female parent may provide bodily secretions originating from glands in or on the body, or from either end of the digestive system (Chapter 8). The few studies of coprophagy to date indicate that this behavior is most prevalent in early instars, suggesting that microbial protein is a crucial dietary component (Chapter 5). The need for animal or microbial protein may help explain why it is difficult to rear many cockroaches in the laboratory. While adults may thrive, "nymphs are more difficult to rear, starving to death in the midst of a variety of food stuffs" (Mackerras, 1970).
As they develop, juveniles may adopt the same diet as adults (e.g., wood, guano in caves) or feed on different materials, such as the rainforest species in which nymphs feed on litter but adults have a more varied menu. Studies in laboratory and urban settings indicate ontogenetic changes in foraging behavior, as well as variation in feeding behavior and food choice within a stadium. Immediately after hatch nymphs of B. germanica are able to find food and return to shelter, but they improve their foraging performance as they age (Cloarec and Rivault, 1991). Periplaneta americana nymphs take large meals during the first three days post-molt, then feed very little until the next (Richter and Barwolf, 1994). Juveniles of Su. longipalpa change their dietary preferences within a stadium. Protein consumption remains relatively low and constant, whereas carbohydrate consumption is highest during the first week, then declines gradually until the end of each instar (Cohen et al., 1987) (Fig. 4.1A). When given a wide range of protein:carbohydrate choices, Rhy-parobia maderae nymphs consistently selected a ratio of approximately 25:75, suggesting that they have the ability to balance their diet (Cohen, 2001). Subadults of B. germanica are impressively capable of compensating dietary imbalances by choosing foods that redress deficiencies (Raubenheimer and Jones, 2006).
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